Electrical control apparatus



March 5, 194 6. c; COLLQM ETAL 2,395,849

ELECTRICAL CONTROL APPARATUS Filed Aug. 7 1943 I5 Sheets-Sheet 2 flzermo tau vie fle meni" IN VEN TOR5.

ENEYS March 5, 1946. c. J. COLLOM ET AL 2,395,849

I ELECTRICAL CONTROL APPARATUS Filed Aug. 7 1945 5 Sheets-Sheet s T ENEYJ.

Patented Mar. 5, 1946 ELECTRICAL CONTROL APPARATUS Cletus J. Collom and Gustav E. Undy, Detroit, Miclm; said Undy assignor to Cletus J. Collom, Detroit, Mich, an individual, doing business as Weltronic Company Application August 7, 1943, Serial No. 497,746

The present invention relates to electric control systems, and in particular provides improved apparatus for controlling an electric welding operation of the resistance welding type.

It has heretofore been proposed to eflect the resistance welding of certain classes of metals by the use of a complete welding cycle which includes a succession of heating and cooling stages, each heating stage being terminated when the work attains a desired temperature, and each cooling stage being terminated when the temperature of the work falls to a desired value. In at least one of the stages the work is brought to a welding temperature, in at least one succeeding stage the work is brought to a temperature within the austenitic temperature range and, preferably, in at least one succeeding stage the work is brought to a temperature appropriate to an annealing action. In what is understood by the present applicants to be the preferred practice of the above system, thermoelectric apparatus is utilized to respond to the temperature of the work and to, consequently, control the terminations of the successive heating and cooling stages. Further, according to the under,- standing of the present applicants, it is preferred that each heating stage comprises a succession of heating and cooling periods, current flow to the work being interrupted, or at least reduced, at least once during each heating stage in the manner described, for example, in the Redmondv Patent No. 2,046,969. In certain instances, also, it is preferred that at least the initial heating period of the initial stage be initiated at a relatively low value of welding current, after which the current automatically builds up to a desired maximum value, so as to afiord a socalled preheating action. In cases, also, where each cooling period is accomplished by a reduction only in the value of welding current, as distinguished from an interruption of such current flow, an autonriatically controlled decrease in cur rent is desired. Y

With the foregoing general considerations in view,. the principal objects of the present invention are to provide a simple, reliable and relatively inexpensive organization of control circuits, well adapted for usein systems such as the above; to provide such a control system embodying improved and simplified arrangements. for automatically adjusting the temperature controlling elements ofithe system to diflerent temperature settings corresponding to the progressof the cycle; to provide such a control system incorporating improved means for providing anautomatic variation in the value of current flowing in a welding circuit, said means constituting improvements upon the arrangements described and claimed in the copending Undy application Serial No. 402,922, filed July 18, 1941.

With the above as well as other objects in view, which appear in the following description and in the appended claims, a preferred but illustrative embodiment of the invention is shown in the accompanying drawings, throughout the several views of which corresponding reference charactors are used to designate corresponding parts and in which:

Figures 1, 2 and 3, collectively. constitute a diagrammatic illustration of a welding system embod'ying the invention; and

Fig. 4 is a view showing the physical relation between the operating coils and the contacts of the series of electromagneticallyoperated relays employed in Figs. 1, 2 and 3. In the latter figures, these coils and relays are shown in separated relation, in order to simplify the drawings.

It will be appreciated from a complete understanding of the present invention that the improvements thereof may be embodied in widely differing welding systems, particularly adapted for widely varying purposes. It is now preferred to embody these improvements in a multistage welding system of the aforesaid type, and, in an illustrative but not in a limiting sense, the invention is so disclosed herein.

Before proceeding to a description or the drawings, it is noted that the conductors which terminate, at the bottom of Figure 1, in the arrowheads designated, respectively, a and c, are directly connected to the conductors which terminate in the correspondingly designated arrowheads at the top of Figure2. Similarly, the conductors which terminate in the arrowheads designated d, e, f, g, h and i, at the'bottom of Figure 2, are directly connected to the conductors having the correspondingly designated arrowheads at the top of Figure 3.

Referring to the drawings, a usual welding transformer WT is provided with a secondary winding, the terminals whereof are directly connected to the electrodes ill and [2' of the associated welding machine. The primary winding of the welding transformer is connected across the line conductors LI and L2, in series with a pair of reversely connected arc discharge devices and R2, which may be and preferably are of the type sold commercially under the trade name-Ignltrons. The characteristics of these devices are 'welliznown and it is thought they require no description except to note that they are normally non-conductive but that, if an igniting potential is applied between the igniters i and the cathodes thereof, during a half cycle of the source in which the anodes 0- thereof are positive, they become conductive and remain so for the balance of the corresponding half cycle of current flow.

In the illustrated system, each heating stage is made up of a succession of heating and cooling periods, the welding transformer WT being supplied with welding current during each heating period, and such current being interrupted during each cooling period. Such current is also interrupted during each of the cooling stages which intervene between successive heating stages. The points in successive half cycles of each heating period at which the corresponding rectifiers RI and R2 are rendered conductive, to thereby energize the welding transformer WT, are determined by a pair of heat control valves V5 and VS, associated with the main rectifiers R! and R2. respectively. Valves V5 and V6 may be and preferably are of a usual three-element, Has-filled type. They are provided with potentiometer tyne r d control circuits comprising a common suppl transformer TIB and individual transformers TI2 and TI3. The tra sformer TI 5 has a usual center-tapped secondary winding conn cted. through a condenser C d. to one terminal of t e rimary wi din s of transformers Ti?! and TI3. T e terminals of the secondary wi din of tr nsformer TIS are connec ed toget er by a brid e co pr sin a condenser CM, a resistor r! and addit ona resistance represented by a air of reverselv connected. hi h vacuum tubes V and V 8. w ich may be of a conventional tyne. The remaining terminals of t e primary windi s of transformers TI2 and TB are connected to t is bridge at the point I4. w ich is between resistor T1 and the plate circuits of valves V1 and V8. It will be no iced. accordingly, that by varying the effe tive values of resistance re resented by valves V1 and V". the relation between the reactance and resistance in the above-mentioned brid e circu t is varied and,

conseouently. the phasev relation between the volta e of tran former TIG and the volta es of transformers T52 and TI3 is correspondingly varied. it being noted that transformers TIZ and TI3 are connected to the bridge circuit in opposed relation to each other. The characteristics of the bridge and associated circuits are also such that when t e resistance of valves V! and V8 is at a maximum value. the voltages of transformers TI2 and T 3 ch values sufficiently high to fire t eir corresponding heat control valves V5 and V5 a point late in half cycles of the welding current. S milarly. when the resistance of alves V! and V R is at a. minimum. the volta es of transformers TI and TI3 reach values sufficient to fire valves V5 and V5 at correspondin ly earlier points in half cycles. As will be understood. the firing points of valves V5 and V5 and. conseouently. of rectifiers RI and R2 may thus be aried over relatively wide ranges correspondin for example, from a full heat value to a value down as low as to of full heat.

The grid-cathode circuit of valve VI includes in. series relation a resistor r8, a phase shifting condenser C13, the potential whereof is controlled. as described below, and a resistor 19. In addition, a smoothing condenser CII -ls preferably directly connected between the grid and cathode of valve V7. The grid and cathode circult of valve VB is similarly connected directly across the phase shifting condenser CI3, in series with resistors rlfl and TI I. Also, a smoothing condenser CI2 is preferably connected directly across the grid-cathode circuit of valve V8, Thus, it will be appreciated that the gridcathode potentials of valves V1 and V8 are at all times determined by the potential of the condenser CI3, and that when this potential is at a maximum, valves V1 and V8 are of maximum re-' sistance (affording a minimum heat setting for the system). When this potential is at a minimum, on the other hand, the resistance of valves V1 and V3 is at a minimum (affording a maximum heat setting for the system).

In the illustrated system, further, the potential of condenser CI3 is automatically varied, to thereby effect an automatic variation in the heat setting of the system. As shown, this automatic variation takes place during only the initial heating stage and functions to automatically increase the heat setting from a minimum value to a maximum value during such initial stage, thereby affording a preheating effect. The adjustment is preferably such that the automatic rise to the maximum heat setting takes place during the initial heating period of such initial stage, although, if desired, the rate of change of the heat setting may be decreased so that an interval corresponding to the over-all length of two or more heating periods and intervening cooling periods is required to complete the full change from minimum heat setting to maximum heat setting, More particularly, the fall and rise of the potential of condenser CI3 is controlled by commutating its connections to a charging circuit comprising potentiometer and a regulating resistor rII, and a discharging circuit comprising potentiometer 1-H and regulating resistor TIE. The commutation of these circuits is controlled by contacts CRIIb and CHI [0 of control relay CRI I, it being noted that when contact CRI I b is closed, condenser CI! is enabled to charge through a circuit which extends from its positive terminal 40 through conductors 20, 22 and 24, potentiometer rl5, resistor rI1, conductor 26, contact CRIIb, 9. normally closed transfer switch 28, and conductor 30 to its negative terminal 42. On the other hand. when relay CRII is energized, its contact CRI lb is open and its contact CRI Ic completes a. discharging circuit for condenser CI3, which includes conductors 20, 22 and 24, potentiometer H4, resistor rI6, contact CRIIc, conductor 82. switch 28 and conductor 30. It will be noticed, also, that the setting of potentiometer rl5 determines the maximum voltage to which condenser CI3 is charged, and that resistor H4 determines the minimum voltage to which condenser CI3 is discharged, both of which values are, of course, obviously adjustable. Resistor H6, in series with potentiometer. rI4. serves to variably determine the rate at which condenser C I3 is discharged from its maximum to its minimum value, and a corresponding control of the charging rate is provided by resistor rIl.

Potentiometers rid and 1'I5 are supplied with voltage from a usual rectifying circuit comprising the continuously energized transformer T20 and a usual full wave rectifier V9. As illustrated, also, this rectifying circuit includes balancing elements comprising the resistor H3 and condenser CH.

As described below, relay CRII is energized at the beginning of the initial heating period of the initial heating stage, and is tie-energized at the end of each welding cycle. During such initialheating stage, the welding current, consequently, rises from a minimum to a maximum value. The rate of change of the current value may be adjusted, as aforesaid, so as to cause the maximum value to be attained at a desired point in such heating stage. In generaL it is preferred to adjust the minimum value to correspond to approximately 20% of full heat, full heat bein: defined as usual as being attained by firing the main rectifiers at the power factor angle of the system. Depending upon the current requirements of the welding load, the maximum value of the heat setting may fall anywhere between 50% and 100% of mu heat.

As shown, the thermoelectric apparatus which is utilized to respond to the temperature of the work and to, consequently, control the length of each heating and cooling stage comprises a thermocouple, the hot junction whereof is afforded'lby the junction between a thermocouple element II4, such as the alloy constantan, and the usual copper electrode I2. The element H4 is iIlustrated as being embedded in the electrode I2, the just-mentioned junction being afl'orded at the work engaging surface of the electrode l2, it being understood that, except at such junction, element H4 is insulated from the electrode I2. The cold Junction of the system is constituted by a multiple adjustment pyrometer I00, which may be and preferably is of conventional construction and which, consequently, is shown in outline form only, The electrode I2 is shown as being permanently connected to the pyrometer input terminal I02, while the element H4 is selectively connectible by means of the arm H2 01' the hereinafter described ratcheting unit to any of a plurality of pyrometer input terminals I04, I06, I08 and H0. As will be understood, when the position of arm H2 is such that input terminals I02 and I04 are. active, a pyrometer setting is afforded which causes it to respond to one temperature of the work. When the position of arm H2 is such that terminals I02 and I06 are active, the pyrometer responds to a. diflerent work temperature, when the position of arm H2 is such that'terminals I02 and I08 are active, the third temperature setting is afforded, and when terminals I02 and H are active, still another temperature setting is pro- ".Vided. In the present system, three heating stages are provided, terminals I04, I06 and I08 corresponding, respectively, to a welding stage, a grain refining stage, and an annealing stage. The remaining terminal IIO serves to determine the temperature to which the work falls during the successive cooling stages.

The pyrometer I00 is provided with a single contact, designated PYa in Fig. 1, which contact occupies the illustrated open position so long as the thermoelectric potential to which 'the pyrometer is subjected is below a value corresponding to the existing adjustment of the pyrometer, butwhich moves to and remains in the closed position so long as such potential is at or above the just-mentioned adjusted value.

The means for operating the arm H2 and the companion arm I26, which, in the illustrated system, controls a forging pressure relay CR8, comprises a ratchet operated drum 58, which is continuously biased to the illustrated .position'by means of a usual spiral spring IN, and which is also provided with a ratcheting pawl I20 and a resetting pawl I22. The ratcheting and resetting pawis are provided with operating solenoids 54 :and 58, respectively, and "in addition the ratcheting unit is provided with a limit switch I24. Switch I24 is biased to the closed position by a spring [25,but is moved to and retained in the open position when the ratchet "drum reaches the illustrated starting position.

It is thought that the remaining details of the system may best be understood from a description of the operation 'of the system asia'whole.

Assuming it is desired to 'e'il'ect a welding operation, the system may be conditioned for operation byclosing the illustrative line switches LSI: and LS2, which connect line conductors LI and L2,:in each of Figs. 1, 2 and 3, to 'a. usualalternating current source of supply. Upon being energized, line conductors Li and L2 complete obvious energizing circuits in Fig. 1, for the primary windings of transformers T3 and 'TII, associated, respectively, with valvesVI and V4. These valves, as well as valve V3, may be and preferably are of the usual three-element, high vacuum type and, as will be understood, they may be provided with usual heating circuits which bring "the cathodes 0 thereof to emissive temperatures. These heating connections have been omitted from the drawings to simplify them. Upon being energized, transformers T3 and TH apply blocking potentials to the grids of the associated valves, and also charge up the associated grid condensers CI and C8. These actions serve to render the corresponding valves I non-conductive, as will be imderstood.

In Fig. 2, the .energization of line conductors LI and L2 supplies energy to transformer T2I, which furnishes filament current to a rectifier, enabling the latter to apply a D. C. potential between terminals 50 and 52, thereby afiording a source of direct current for operating the windings 54 and 56, associated with the ratchet unit 58.

In Fig. 3, the energization of line conductor LI and L2 supplies, through obvious circuits, energizin current for the filament transformers'TH and TI5, associated with the filament circuit of valves V5 and V6. As obvious circuit is also completed for transformer T", which supplies filament current for valves'V'l, V8 andVS.

The energization of line conductors L'l and L2 (Fig. '3) also energizes transformer T20, which thereupon, through rectifier V9, applies a fixed potential across potentiometers H4 and H5,

which action results in charging condenser CI3 to its maximum value, the charging circuit extending through resistor .rI5 -and the now closed back contact CRI Ib of relay CRI I. IAsaforesaid, the potential of condenser CI3 negatively biases valves V1 and V8, and being at a maximum value, substantially-a maximum resistance is afforded by valves V1 and V8.

The energization of line conductors LI and L2 (Fig. 3) also energizes transformer TI6, which, through the previously described bridge circuit, energizes grid transformers "'Il2 andTIS, associated withvalves V5 and V6. These potentials, which are at a phase position corresponding to approximately a minimum heat setting of the system, tend, during successive half cycles, to fire valves V5 and V6. Under the conditions stated, however, the plate circuits of these valves are interrupted at the now open contacts CRI2a and CRIZb of relay CR1 2, so that no current ispasse'd by these valves. 1

Assuming it is desired to 'eifect a welding operation, the workpieces W may be lntroducedbetweenthe electrodes 10 and I2, after which the pilot switch PI may be closed. Pilot switch PI serves to afford a complete welding cycle having the aforesaid welding, refining and annealing stages, and closure of this switch completes an obvious energizing circuit for a usual solenoid opera-ted fluid-control valve 60, which action may, in any desired manner, serve to cause the electrodes to move into clamping engagement with the work at a pressure suitable for welding.

Closure of pilot switch PI, also, through conductor 68, directly energizes transformers TI and T2, associated with valve VI. Upon being energized, transformer T2 opposes the previously energized blocking transformer T3 and enables the energy stored in condenser CI to discharge through the associated resistor rI At the expiration of a discharge period, proportioned to be long enough to enable the full movement of the electrodes into the clamping position, valve VI becomes conductive, enabling the now energized plate transformer TI to pass current therethrough and energize control relay CR2. Upon being energized, relay CR2 closes its contacts CRZa and CRZb. Closure of contact CRZb (Fig. 2) prepares a circuit for control relay CR1, which action is without immediate effect. Closure of contact CRZa prepares a circuit for transformer T.', which circuit remains incomplete, however, pending closure of the companion pilot switch P4.

Assuming it is desired to initiate the weld, pilot switch P4 may be closed, which action directly completes a circuit for relay CRI, subject only to the now closed back contact CRIa of relay CR'I. Upon being energized, relay CRI closes its contacts CRIa, CRIb and CRIc. Contact CRIb directly completes a holding circuit for relay CRI. in parallel with switch P4, which may thereupon be released to the open position without affecting the cycle now in progress; and in conjunction with contact CRIa, completes a holding circuit for valve 60. Completion of the latter holding circuit enables switch PI to be released without effect.

The closure of switch P4 also completes a circuit (which is held closed after the opening of switch P4 by contact CRIb) for transformer T1, associated with valve V3. Upon being energized, transformer T1 applies anode potential to the normally conductive valve V3 and passes current therethrough to energize control relay CR4. Upon being energized, relay CR4 closes its contacts CR4a and CR4b, which contacts are connected in series relation with each other. Closure of contact CR4a completes a circuit through conductor 82 for the coil of relay CRI I, which circuit also includes the now closed back contact CRla of relay CRT, which thereupon closes its contacts CRI Ia and CRI I0, and opens its contact CRI lb. The effect of contacts CRIIb and CRI I i described below, but closure of contact CRI Ia completes a self-holding circuit for relay CRI I, which holding circuit, however, includes the now closed contact CRI b of relay CRI Closure of contact CR4a in conjunction with contact CR4b energizes the firing relay CRI2, through a circuit which includes, in series relation, the now closed back contacts CR5a and CRIa of relays CR5 and CR1. Upon being energized, relay CRIZ closes its contacts CRI2a and CRIZb. Closure of contact CRIZa and CRIZb (top of Fig. 3) applies anode potential to the firing valves V5 and V6. The circuit for valve V5 extends from line conductor LI through conductor 90 (bottom of Fi 2 and top of Fig. 3), contacts CRIZa, valve V5, conductor 92 (bottom of Fig. 2 and top of Fig.

3), igniter i and cathode c of main rectifier RI, and thence through conductor 94 and the primary of the welding transformer WT to line conductor L2. Closure of contact CRIZb completes a similar circuit through which potential is applied across valve V6 and it will be noted that in these circuits, valves V5 and V6 are connected, respectively, in parallel with th anode-igniter circuits of main rectifiers RI and R2.

It will be recalled from previous description that, during each successive positive half cycle and, with the initial adjustment of the system, at a point therein which corresponds to about 20% full heat, transformer TIZ applies a conductive potential to the grid of valve V5, tending to render this valve conductive. At a corresponding point in each negative half cycle, a conductive potential is applied to the grid of valve V6 by transformer TI3. Depending upon whether the closure of contacts CRl2a and CRI2b takes place during a positive or a negative half cycle, therefore, either main rectifier RI or main rectifier R2 is the first main rectifier to be fired. Assuming such closure occurred during a positive half cycle, the potential applied to valve V5 passes current therethrough and passes an igniting current between the igniter i and the cathode c of rectifier RI, which action, a will be understood, fires this valve and initiates the flow of welding current. At the corresponding point in the succeed ing negative half cycle, rectifier R2 is fired through valve V6 and so long, therefore, as contacts CRI2a and CRI2b remain closed, rectifiers RI and R2 are effective to pass current to the welding circuit at a. heat setting determined by the phase shift adjustment of transformer TIZ and TI 3.

Upon being energized, as aforesaid, and simultaneously with the energization of relay CRI2, relay CRII opens its back contact CRlIb and closes its front contact CRI la. The former action interrupts the circuit for condenser CI3, which includes the minimum heat setting potentiometer rl5. On the other hand, closure of con tact CRI Ib completes the previously described discharge circuit for condenser CI3, which circuit includes potentiometers H4 and rIS and through which circuit condenser CI3 is enabled to gradually discharge to the minimum potential determined by potentiometer rI4, at a rate determined by resistor rIB. In response to this action, the potential across condenser CI3 gradually falls from its normal or maximum value towards its minimum value. The progressive decrease in potential across condenser CI3 is reflected as a decrease in the negative grid bias potential of valves V1 and V8, which action correspondingly and gradually decreases the resistance of these valves and alters the ratio of reactance to resistance in the bridge circuit to which transformer TI! and TI3 are connected. As aforesaid, this shift gradually advances the points in successive positive and negative half cycles at which valve V5 and V6 are rendered conductive. This, in turn, advances the point in such half cycles at which rectifiers RI and R2 are fired, and correspondingly increases the value of the welding current.

In addition to the operations described above. closure of contacts CR4a and CR4!) of relay CR4 completes an energizing circuit for the grid transformer TB associated with valve V3, which action blocks this valve and interrupts the supply of cur; rent to relay CR4 from anode transformer T1. In respons to this action, the energy stored in the coil of relay CR4 starts to discharge through the associated condenser C4 and at. the expiration at a u'edetermiried heating. period relay CR4 re.-

- sumes the: de-energized. position, opening its.- contacts CR4a and CR); In view of the holding circuit. afforded by con-tact CRHa, this action is without effect. on the phase shift control relay CE! I, which, consequently, continues. tomaintain the. circuit connections corresponding to. a minimum potential of. condenser GL8. The. opening of. contactsv CRM and CR; does, however, deencrgize relay CRI2, which thereupon reopens its contacts CRI 2a and CRHb. The opening, oi these contacts interrupts the anode cimcuitsof the fir.- ing valves V and V6, which thereupon become inefiecti-ve toapply firing potentials tothe. main rectifliersRl. and B2. In view of the known charactor of the: latter rectificrs' the interruption: of these anode circuits has no effect on. a flow of current then in progress-through one Or the: other at the rectifiers RI and R2. Such action does, however, cause, the flow of welding current to be terminated at the endof the half cycle. then in progress, and: prevents a re-initiation of the flow of. welding current duringasucceeding, half: cycle.

The opening of contacts CR4; and. CRAb also tie-energizes gridtransformer' T8,. enabling the energy; now stored. in condense C5 to start dis,- charging through the local circuit, including; resister; r3. At. the expiration of a predetermined discharge period, valve. V3 againbecomes conductive. enabling. transformer T1 to ire-energize relay CRL. This action duplicates the action which. resulted from the initial, energization. of relay CR4 in so far a concerns the; re-energization of. the firing relay CR I l, and the consequent rte-initiation of the flow of welding; current, except: that in this instance the ire-initiated weldin: current isv of a value corresponding; to. the now existing. potential of. condenser (313;. As. aforesaid, in many cases. it, is preferred to adilust the system so that. the charging rate; of condenser C13 is such. that themaximum heat. setting is. attained during. the. initial heating; period, in which event, the; just-mentioned second heating, period is: initiated at a. full heat, setting. The: reenergizatiorr. oi relay 6R4; also: ire-energizes trans." former T8 and applies ablocking potential to the grid: of valve V3. action again. initiates a timing out of relay CR4, at the expiration of which it resumes. the tie-energized position, as

befmza, So; long, thereforaes transiormer'lft re.-'

mains energized, relay CR4 pulsates between an energized; position: and a tic-energized. position, the energized interval being determined by con.- densen C4; and th (lo-energized interval being determined, by condenser C5. Each energized in.-' tonval. in. turn, afiords a. heating, period during whichv current flows to. the welding circuit; and each. de-energized; interval affords; a coolingv period during which such current flow is. prevented.

As:- thus far described, accordingly,v closure of pilot switches PI- and. P4 has brought the electrodesinto. engagement with the work with. a welding; pressure, and has initiated a flow of welding current to the work, which flow of weld.- ing current takes place as. a succession of: separated; heating periods, each heating period com.- prisinga desired fraction of. each of. a. plurality of half cycles of the source. This flow of welding current. continues. until interru-ptedv by the temperature. responsive elements which, in coniunctiontwith. the ratcheting device- 56, serve to. determinathenumher oi stagestemperatures attained in the succesive; stages and the. temperatures attained, in the intervals between successive stages.

Continuing, now with the description. of the operation, the. initial. energization of relay CRI', which. results fromthe closure of pilot switch P4 at the. beginning of the welding cycle, also causes this. relay to close its front contact CR l e. This action completes. a circuit through the now closed series. connected back contacts. CRB'b and CR5c for the winding 54, associated with the advancing pawl oi the ratchet. unit. This circuit serves to apphz the rectified potential between terminals 50 and 52' to winding. 54, through conductorsv I30, l3.2, a. portion of line conductor LI and the abovementioned. contacts. Upon being, energized, winding 54' advances pawl [.20 and moves the ratchet unit to its first operating position, in which. arms. I I2. and 1'26 engage terminals bl. and at, respectively. The latter engagement is without. effect, but the; former engagement. connects input terminals [02 and [M to the thermocouple afiorded by the electrode. 12. and the embedded element. 4.. The flow of welding current. initiated as described above, causes the temperature. of. the work to. progressively rise, which rise in. temperature, taking place during. the. course of successive heating periods. of the. initial heating, stage, is, reflected as an increasing, thermoelectric E. M. FL. between terminals. [.02 and. HM. When this temperature reaches. a welding value, appropiate tov the formation of a. weld nugget between the. workpieces, pyrometer I responds and immediately closes its. contact PY'a, Referring. to Fig, 1, this action. immediately energizes relay CR6 and transformers T9. and THL. associatedi with valve. V4,. Upon. being energized, re.- lay CR6 opens its contact CRBli and closes. its contact CRS'a. The opening 0t contact CRBb interrupts. the. previously traced energizing circuit for solenoid 5. L, enabling the. spring associated, with pawl L20. to. withdraw it to a position in which it, engages. behind thenext successive tooth of. the ratchet. drum, this action being preparatory to. an advancing movementof the ratchet unit.

Upon being energized, transformer TH) opposes the continuously energized transformer TH and enables the energy stored in condenser C6 to discharge through. the. local circuit comprising resistor. 1. At the. expiration of a short interval,,of. the. order of a. cycle or two, sufficient only to. allow the above-mentioned withdrawal of the. pawl I15, valve V4. becomes. conductive. This action enables transformer T9 to pass: current therethrough and energize v relay CR5, which thereupon opens its. contacts-0125a and CREc. and closes its. contact CRSD The. opening of contact CRicis without immediate. eilect, since. contact CRBa (near the topof. Fig. 2). This action energizes. a. usual. forging, pressure valve 152, resulting, any suitable way, in the application to the work of a substantially higher or forging pres.-

sume.

The. transfer movement. of H2 interrupts the pyrometer input circuit between. terminals I02; and IM and. completesan. input circuit. between terminals tfll and H0... transfer movement is quiterapidaind,v due to the. sluggish character. of the pyrometer W0, is completed before contact PYa has an opportunity to open. As soon as the transfer movement is completed, the pyrometer is readjusted to a materially lower temperature, (preferably, to a temperature well below the annealing temperature of the work) and, consequently, maintains its contact PYa closed until such materially lower temperature is attained.

The opening of contact CRa immediately interrupts the energizing circuits for transformer T1 and for firing relay CRI2. It will be noted that this action may take place either during a heating period or during a cooling period, since it is found in practice that the temperature of the work may continue to build up at least throughout the initial portion of a cooling period. Consequently, the critical operating temperature, at which the pyrometer responds, may be attained during a cooling period. If the pyrometer responds, during a cooling period, the opening of contact CR5a is without immediate effect, since under these conditions, relays CR4 and CRI2 are already de-energized. In such instance, the opening of contact CR5a serves only to prevent the re-energization of relays CR4 and CRI2 and, consequently, prevents the initiation of a heating period at the conclusion of the cooling period then in progress.

On the other hand, if the pyrometer responds during a heating period, the consequent opening of contact CREa immediately de-energizes relay CRI2 and thereby interrupts the fiow of welding current, terminating the first heating stage, and initiating the first cooling stage. In such case, also, the deenergization of transformer T1 is without immediate effect on relay CR4 because of the holding action of condenser C4, but does prevent the re-energization of relay CR4.

When the temperature of the work has fallen to the aforesaid low value, preferably well below the annealing temperature of the work, the pyrometer contact PYa resumes its open position, which action immediately de-energizes relay CR6, transformer T9 and transformer TIO. The deenergization of relay CR6 causes its contacts CREa and CRBb to resume the illustrated positions, Reclosure of contact CRIib prepares the original energizing circuit for ratchet winding 54, and the opening of contact CRBa interrupts the last traced circuit for winding 54. In response to this action, pawl I20 is withdrawn to a position in which it engages behind the next ratchet tooth, preparatory to the next ratcheting step.

The de-energization of transformer TIO enables the continuously energized transformer TI I to apply a blocking potential to the grid of valve V4, which action interrupts the original energizing circuit for relay CR5 and enables the energy stored in the coil thereof to discharge through the local circuit comprising condenser C6. At the expiration of a short period, sufficient only to allow the above resetting movement of the ratchet pawl I20, relay CR5 resumes the de-energized position, restoring its contacts CR5a, CR5b and CR5c to the illustrated positions. The transfer action of contacts CR5!) and CR5c recompletes the original energizing circuit for winding 54, which thereupon acts to advance the ratchet drum to the third operating position in which arms I I2 and I26 engage terminals 123 and a3, respectively.

When arm I26 moves away from terminal a2, it interrupts the circuit for relay CR8, which thereupon resumes the deenerglzed position. This action de-energizes the forging pressure valve I52, restoring the electrode pressures to the lower or welding value. In the sequence now being described, the engagement of terminal a3 by arm I26 is without effect.

The engagement of arm II2 with terminal b3 connects terminals I02 and I06 to the thermocouple, which terminals, as aforesaid, adjust the pyrometer to a temperature appropriate to a grain refining heat. This adjustment makes no change in the now open position of the pyrometer contact PYa, since this grain refining temperature is well above the pre-existing temperature of the work.

The reclosure of contact CR5a completes the original energizing circuit for transformer T1, associated with valve V3. Upon completion of this circuit, relay CR4 is again energized and initiates the second heating stage in the manner described with reference to the first stage, with the exception that in this instance the energized relay CRII has already caused the phase shift condenser CI3 to establish the maximum heat setting for the system. It is believed that it will be evident that during this second stage, relay CRI2 is again pulsated between energized and de-energized conditions, so as to provide successive heating and cooling periods in the same manner that these periods are provided during the initial or welding stage. Also, when the work attains the grain refining temperature, the Pl!- rometer responds, as before, to initiate the sec- 0nd cooling stage. In this case, the initiation of the second cooling stage involves advancing the ratchet arms into engagement with terminals b4 and a4, respectively. The latter action again energizes the forging pressure relay CRO, which acts to apply the forging pressure to the work. The engagement of terminal b4 again adjusts the pyrometer for its minimum temperature corresponding to the temperature attained at the expiration of the first cooling stage.

At the expiration of the second cooling stage, also, the third heating stage is initiated in the same manner that the second stage was initiated, except that in this case, the ratchet arms advance into engagement with terminals b5 and a5, respectively, it being understood that terminal b5 adjusts the pyrometer for the third or annealing stage.

During the course of the third heating stage, relay CRI2 is again pulsated in the previously described manner, it being noted, of course, that the second stage may be expected to include fewer heating and cooling periods than the first stage, and that the third stage may be expected to include fewer such periods than the second stage.

The third cooling stage also proceeds in the previously described manner and at the conclusion thereof the system is reset to its original condition as follows.

When the minimum temperature corresponding to the pyrometer input terminal III! is reached, the pyrometer contact PYa again opens and, as before, by virtue of the reclosing of contacts CRGb and CR5b, the ratcheting unit is advanced to its seventh position, in which the arms I26 and H2 engage terminals a! and N. The terminal N is an inactive terminal in the operation now being described.

The movement of arm I26 out of engagement with terminal a6 again de-energlzes the forging pressure relay CR8, restoring the electrode pressure to the normal or welding value. Its movement into engagement with terminal a! completes the circuit, subject to the now closed contact CRZa for the resetting relay CR1. In response to this action, relay CR1 assumes the energized position, closing its contacts CRIb and CRI'c and opening its contact CR'Ia. The opening of contact CRIa immediately interrupts the circuits for relays CRI, CRII and CRI2, and also interrupts the circuits for anode transformers TI and T1, associated, respectively, with valves VI and V3. The interruption of the circuit for relay CRI2, at contact CRla, prevents the re-energization of this relay, which re-energization normally occurs at the expiration of a cooling stage, and thus terminates the welding cycle. The interruption of the circuit for relay CRI I causes this relay to resume the illustrated position. This action, at contacts CRI Ic and CRI Ib, interrupts the discharging circuit for the phase shifting condenser CI3 and recompletes the original charging circuit therefor, preparatory to the next welding operation. Closure of contact CR'Ib completes a circuit for the resetting winding 56, associated with the ratchet unit, which thereupon withdraws the pawl I22 from engagement with the ratchet drum, preparatory to the return movement of the drum.

It is to be noted that the de-energization of relay CR5, which resulted from the opening of contact, PYa at the conclusion of the final cool period, not only energizes relay CR1, as aforesaid, but, at contact CRSa, tends also to recomplete the circuit for transformer T1, thereby tending, through the consequent sequential energization of relays CR4, CRII and CRI2, to re-initiate the flow of welding current. Such recompletion may be prevented by providing a slight delay in the closing movement of contact CR5a, suilicient to enable the opening of contact CR'Ia, to precede such closure. Even in the absence of such time delay on contact CR5a, the recompletion of the circuit for transformer T1 is oi a momentary character only. In practice it is found that by virtue 01 its relatively heavier character, the

firing relay CRI2 does not have time to reach the closed position before its circuit is opened by the opening of contact CRIa. If desired, suitable means may be provided to delay the closure of contactor CRI2.

Continuing with the resetting action, the deenergizatlon of relay CRI causes its contacts CRIa, CRIb and CRIc to re-open. The latter contact de-energizes operating winding 54 of the ratchet unit, and enables the associated return spring to restore it to the illustrated starting posiiton, in which the arms I26 and H2 are out of engagement with their associated commutator terminals. At the conclusion of this return movement, the cam I23 on the ratchet drum opens the limit switch I24, thereby de-energizing the reset winding 56.

The return sweep of the arm II2 sequentially reconnects the terminals IIiI, I08, I06 and I04, which action'is, however, Without effect, since the work is now below the temperatures to which these terminals correspond. The return sweep of the arm I26 causes it to momentarily complete circuits for the forging pressure relay CR8, but this return movement is so rapid that the relay does not remain energized long enough to have any eflect. The return sweep of the arm I26 also interrupts the initially traced circuit for relay CRI, which action is, however, without effect in view of the holding effect of the now closed contact CRlc, which is connected in parallel with arm I26.

Contacts CRIa and CRIb. in opening, further interrupt the circuit for transformer TI and also interrupt the previously traced holding circuits in parallel with the pilot switches PI and P4. In. addition, the opening of contacts CRIa and CR") interrupts the circuit. for the welding. pressure valve 60, which thereupon relieves the welding pressure from the work and enables the work to be removed from or adjusted in the machine, preparatory to the making of the next weld.

The de-energization of transiormer TI deenergizes control relay CR2, which thereupon resumes the de-energized position, opening its con. tacts CR2a and CR2b. The re-opening of contact CRZa is without efiect, in view of the previous opening of contact CRIa, but the re-opening of contact CR2!) interrupts the previously traced holding circuit for the resetting relay CR1, which thereupon resumes the illustrated position without efiect. The above-described resetting operations serve to restore the system to its normal condition, in readiness for the next welding operation.

A welding operation comprising only two heating and two cooling stages may be eflected by closing pilot switch P2. The resulting operations are the same with the exception that such closure directly energizes relay CR9 (top of Fig. 1). Relay CR9, in turn, through its contact CRIIa, energizes valve 60 and performs the other operations previously attributed to switch PI. Upon being energized, relay CR8 also closesits contact CRQb, which serves, as shown in- Fig. 2; to connect the coil of relay CR1 to the commutator terminal a5.

It will be recalled that the arm I26 moves into engagement with thisterminal immediately following the conclusion of the second cooling stage. Since, also, the energization of relay CR1 terminates the welding operation, as described above, it will be appreciated that by energizing this relay, iollowing the second cooling stage, the cycle may be limited, as aforesaid. Also, a single stage operation can be efiected by closing pilot switch P3, which action, in addition to the other described operations, energizes relay CRI'I. Ii relay CRIB is energized, its contact CRIUb connects the coil of relay CR1 to the commutator terminal a3. It will be recalled that this terminal is engaged at the conclusion of the first cooling stage.

Although only a single embodiment of the invention has been described in detail, it will be appreciated that various changes may be made therein within the spirit and scope of the invention.

. What is claimed is:

1. In a control system for controlling flow of current between a work circuit and a source of periodic current, electric valve means for controlling said flow, control means for actuating said valve means to enable said flow during a succession of periods of said source, means for causing the portions of the said periods throughout which said flow occurs to vary in accordance with a predetermined pattern, said varying means including an energy storage device, means including circuit connections for providing control circuits through which said device may respectively be charged and discharged, said portions being progressively increased when one oi! said control circuits is effective and being progressively decreased when the other of said control circuits is eflective, and means for commutating said connections.

2. In a control system for controlling flow of current between a work circuit and a source of periodic current, electric valve means for controlling said flow, control means for actuating said valve means to enable said flow during a su(: cession of periods oi said source, means for causing the portions of the said periods throughout which said flow occurs to vary in accordance with a predetermined pattern, said varying means including an energy storage device, means including circuit connections for providing control circuits through which said device may respectively be charged and discharged, said portions being progressively increased when one of said control circuits is effective and being progressively decreased when the other of said control circuits is efiective, and means for commutating said connections, one of said commutating and control means being operably responsive to the other.

3. In a control system for controllnig flow of current between a work circuit and a source of periodic current, electric valve means for controlling said ilow, control means for actuating said valve means to enable said flow during a suc cession of periods of said source, means for caus ing the portions of the said periods throughout which said flow occurs to vary in accordance with a predetermined pattern, said varying means including an energy storage device, means including circuit connections for providing control circuits through which said device may respectively be charged and discharged, said portions being progressively increased when one of said control circuits is effective and being progressively decreased when the other of said control circuits is effective, and means for commutating said connections, said varying and commutating means operating in timed relation to each other.

4. In a control system for controlling flow of current between a work circuit and a source of periodic current, electric valve means for controlling said fiow, control means for actuating said valve means to enable said flow during a. succession of periods of said source, means for causing the portions of the said periods throughout which said flow occurs to vary in accordance with a predetermined pattern, said varyin means including an energy storage device, means including circuit connections for providing control circuits through which said device may respectively be charged and discharged, said portions being progressively increased when one of said control circuits is effective and being progressively decreased when the other of said control circuits is effective, and means for commutating said connections, said commutating means being operably responsive to said control means.

5. In a system for controlling flow of current between a source of power and a work circuit, the combination of means enabling said flow during each of a succession of intervals, each interval being of controllable length, means individual to each interval for controlling the duration thereof, indexing means for selecting said individual means, and means operated as a consequence of the initiation of current flow in one said interval for actuating the indexing means and controlling the initiation of current flow during a succeeding interval.

6. In a system for controlling flow of current between a source of power and a work circuit, the combination of means enabling said flow during each of a succession of intervals, each interval being of controllable length, means individual to each interval for controlling the duration thereof, indexing means for selecting said individual means, control means actuable to initiate flow of current during an initial said interval, and means operated as a consequence of the actuation 01' said control means for adjusting said indexing means to correspond to the next said interval.

'7. In a system for controlling flow of current between a source of power and a work circuit, the combination of means enabling said flow during each of a succession of intervals, each interval being of controllable length, means individual to each interval for controlling the duration thereof, indexing means for selecting said individual means, control means actuable to initiate flow of current during an initial said period, and means operated as a consequence of the actuation of said control means for adjusting said indexing means to correspond to the next said interval, said adjustment being made at the conclusion 0! said one interval.

8. In a system for controlling flow of current between a source of power and a work circuit, the combination of means enabling said flow during each of a succession of intervals, each interval being of controllable length, means individual to each interval for controlling the duration thereof, indexing means for selecting said individual means, and means operated as a consequence of the initiation of current flow in one said interval for actuating the indexing means and controlling the initiation of current flow during a succeeding interval, said indexing means comprising means operated in accordance with a physical characteristic of the work circuit which varies as a consequence of the flow of current therethrough.

9. In a system for controlling flow oi current between a source of power and a work circuit, the

combination of means enabling said flow during 

